Rheology of organoclay assisted extrusion of HDPE using particle image velocimetry

Abstract

Wall slip is often seen as a source of flow enhancement and can play a significant role duringcertain melt instabilities in polymer processing. In the present investigation, the effect oforganoclay on the wall slip of high density polyethylene (HDPE) was investigated with theaid of particle image velocimetry (PIV). The study showed that organoclay did not causesignificant wall slip during low shear testing in a parallel plate rheometer. However, PIVmeasurements showed that organoclay induced more wall slip during continuous extrusionof HDPE. Also, reduction in the extrusion pressure and elimination/postponement of meltinstabilities in HDPE during continuous extrusion were observed. There was good agreementbetween the flow curves obtained from PIV and rheological measurements. In the presenceof high shear flow, organoclay was suggested to align in the flow direction and migratetowards the die wall. The alignment and migration affect the bulk rheological properties(increase in shear thinning) and surface properties (increase in wall slip) of HDPE.